I'd appreciate any tips on how to use auto-focus aim-points for birds in flight.

I've been only using the center point, but it's often hard to keep small fast or erratic flying birds right on the aim point with my 500L and 5dII. I've tried using all the aim-points only once and couldn't figure out what the camera was doing as a subject crossed from point to point as I waved the camera around at it.

Is there some combination of aim-point selected and, perhaps, focus limitation that works best? Some other method?

I was using my sigma 150-500 at an air show, and I gave up on AF. I think it best to manual focus at infinity and use a narrow aperture. (You might be able to set a hyperfocal distance, too.) The AF beep when I set the exposure was reassuring. But the images were still not as sharp as I thought they should be.

I gave up on trying to focus manually when my hit rate was around 1%. AF is doing better using the center aim point, maybe as much as 10% hit rate and when I get a hit it is much more nearly critically sharp.

I'm wondering if one of the other AF modes in the 5dII would be better than center point, servo mode. My testing has been inconclusive, but maybe I'm not using it right.

With the 7D I usually select the center AF zone with "af zone expansion". That measn it tries to AF using the center zone, but if it can't get a focus lock or the subject moves out of the zone, 4 adjacent AF zones which surround in the center zone come into play.

I don't have a 5D2, but it would seem to correspend to something like "C.Fn III -7 – AF expansion with selected point" on the 5D2.

I don't think hyperfocal focusing would work well and manually tracking a bird in flight is very tricky. I think you'd need at least a gimble lens mount so you could aim with one hand and focus with the other. Even then I think AF is still going to beat you most of the time.

I have a 5DII and I have tried a 7D ... the 7D has a huge upper hand on the 5DII on autofocus for action in good light. The 5DII has a huge upper hand on autofocus in near darkness. I do not recommend the 5DII for action. I find the autofocus and frame rate are not sufficient.